Data from: Evidence of host-associated divergence from coral-eating snails (genus Coralliophila) in the Coral Triangle

We studied how host-associations and geography shape the genetic structure of sister species of marine snails Coralliophila radula (A. Adams, 1853) and C. violacea (Kiener, 1836). These obligate ectoparasites prey upon corals and are sympatric throughout much of their ranges in coral reefs of the tropical and subtropical Indo-Pacific. We tested for population genetic structure of snails in relation to geography and their host corals using mtDNA (COI) sequences in minimum spanning trees and AMOVAs. We also examined the evolutionary relationships of their Porites host coral species using maximum likelihood trees of RAD-seq (restriction site-associated DNA sequencing) loci mapped to a reference transcriptome. A maximum likelihood tree of host corals revealed three distinct clades. Coralliophila radula showed a pronounced genetic break across the Sunda Shelf (Φ CT = 0.735) but exhibited no genetic structure with respect to host. C. violacea exhibited significant geographic structure (Φ CT = 0.427), with divergence among Hawaiian populations, the Coral Triangle and the Indian Ocean. Notably, C. violacea showed evidence of ecological divergence; two lineages were associated with different groups of host coral species, one widespread found at all sites, and the other restricted to the Coral Triangle. Sympatric populations of C. violacea found on different suites of coral species were highly divergent (Φ CT = 0.561, d = 5.13%), suggesting that symbiotic relationships may contribute to lineage diversification in the Coral Triangle.

本研究探讨了宿主关联与地理格局如何塑造一对姊妹海洋螺类物种——齿珊瑚螺（*Coralliophila radula* (A. Adams, 1853)）与紫珊瑚螺（*Coralliophila violacea* (Kiener, 1836)）的遗传结构。这两类专性外寄生生物以珊瑚为食，在热带、亚热带印度-西太平洋珊瑚礁的大部分分布区内均为同域分布。本研究基于线粒体DNA（mtDNA）的细胞色素氧化酶亚基I（COI）序列，通过最小生成树分析与分子变异方差分析（AMOVA），检测了螺类种群遗传结构与地理分布及宿主珊瑚的关联性。此外，本研究通过比对参考转录组的限制性酶切位点相关DNA测序（RAD-seq, restriction site-associated DNA sequencing）位点构建最大似然树，分析了其宿主石珊瑚属（*Porites*）珊瑚的系统演化关系。宿主珊瑚的最大似然树显示存在3个独立演化支。齿珊瑚螺在巽他陆架区域存在显著的遗传分化断点（ΦCT = 0.735），但未呈现与宿主相关的遗传结构。紫珊瑚螺则呈现显著的地理遗传结构（ΦCT = 0.427），夏威夷种群、珊瑚三角区及印度洋种群间均存在遗传分化。值得注意的是，紫珊瑚螺存在生态分化的证据：两个演化支分别关联不同类群的宿主珊瑚，其中一支广布于所有采样位点，另一支仅分布于珊瑚三角区。同域分布的紫珊瑚螺种群若宿主珊瑚类群不同，则遗传分化程度极高（ΦCT = 0.561，净遗传距离d = 5.13%），这表明共生关系可能推动了珊瑚三角区的类群分化。